Presence Of More Particles Research Articles

On quantum electrodynamic processes in plasmas interacting with strong lasers

In the realm of laser-plasma interactions, if the laser intensity is strong enough, quantum effects play a significant role. Due to the large separation between the length scale at which quantum electrodynamic processes form and both the typical separation between particles in a plasma and the wavelength of optical lasers, it is possible in many situations of interest to take into account quantum electrodynamic processes in a fairly straightforward way. If one considers plasmas of increasingly large densities, the presence of many particles can render potentially unavoidable a full quantum treatment of the dynamics. Here, two kinds of multi-particle effects are discussed within strong-field Quantum Electrodynamics. First, we show how a correct description of coherence effects in the radiation emitted by a two-electron wave packet in a strong laser field requires a quantum treatment also if the quantum nonlinearity parameter of the system is much smaller than unity. Secondly, we indicate that at solid-state densities the presence of several particles within the formation region of radiation by an electron in a strong electromagnetic field may alter the emission probability itself, such that in general it is not possible to disentangle collective effects from quantum effects.

Study of Electron Beam on Electron Cyclotron Waves with AC Field in the Magnetosphere of Uranus

In this paper, we investigate the electromagnetic electron cyclotron (EMEC) waves in the magnetosphere of Uranus. By using the method of characteristic solution, the expression for dispersion relation is drawn. Following kinetic approach, the growth rate and real frequency of EMEC waves is studied theoretically, considering the injection of cold plasma beam in the Uranian system. The observations made by a space probe launched by NASA, Voyager 2, showed unusual orientation of planet’s spin axis and presence of more particles in high energy tail in Uranian magnetospheric plasma. Therefore, in this paper Kappa distribution is employed instead of usual Maxwellian distribution. The study is extended to the parallel as well as the oblique propagation of EMEC waves with variation in temperature anisotropy, number density of electrons and angle of propagation with respect to magnetic field direction. It is found that these parameters support the growth rate of EMEC waves. But response of real frequency of these waves is not same as that of growth rate for all the cases. Numerical analysis also revealed that as the ratio of number density of cold to hot plasma increases growth rate of EMEC waves also increases. Thus, denser the beam is injected, more the growth can be observed. These results are appropriate for applications to space plasma environments and magnetospheric regimes for detailed comparative planetary study.

Dynamic wettability evaluation of nanoparticles-coated surfaces

The present study concerns an investigation on the variation of wettability of flat aluminum plates covered with porous thin-films of nanoparticles. Since the contact angle of the obtained surfaces is small, and in many cases the deposited droplet has not achieved a static state, dynamic top-down analyses of spreading droplets were performed. Surface roughness and morphology of the deposited layers were also investigated, in order to provide additional information about the nanotextured surfaces that could be related to their wettability behavior. Aluminum oxide (20–30 nm and 40–80 nm) and silicon oxide (15 nm and 80 nm) nanoparticles were deposited on aluminum plates through a nucleate boiling process. Depositions were obtained through pool boiling of water/Al2O3 and water/SiO2 nanofluids containing 0.01%, 0.1% and 0.5% in volume of nanoparticles. According to the wettability evaluation, a change in spreading mechanism could be identified, varying from inertially-driven during the first few milliseconds to capillary-driven effects, which in some cases sustained the spreading process even after 1 s. Although deposition of nanoparticles has generally increased surface roughness, no relation between roughness and wettability was found in the present investigation. On the other hand, super-wetting behavior was related to the presence of more particles’ clusters on top of the surfaces, possibly enhancing the connections through porous layers.

Localization due to interaction‐enhanced disorder in bosonic systems

Localization in interacting systems caused by disorder, known as many‐body localization (MBL), has attracted a lot of attention in recent years. Most systems studied in this context also show single‐particle localization, and the question of MBL is whether the phenomena survives the effects of interactions. It is intriguing to consider a system with no single‐particle localization but which does localize in the presence of many particles. The localization phenomena occurs “due to” rather than “in spite of” interactions in such systems. We consider a simple bosonic system and show that interactions enhance the effects of very weak disorder and result in localization when many particles are present. We provide physical insights into the mechanism involved and support our results with analytical and numerical calculations. image

The Floatability of Single Spheres versus Their Pairs on the Water Surface.

Particle floatability at the water surface encountered in nature and industrial systems often occurs in the presence of many particles, but the available theoretical developments are based on the flotation of single particles. Here experiments were conducted to compare the floatabilities of single and multiple spheres on the air-water interfaces. Specifically, the forces on floating single spheres and their pairs versus the depth of deformed interface were measured using a force sensor combined with high-speed video microscopy and modeled based on the 3D Young-Laplace equation which was numerically solved. The experimental and theoretical results for the vertical forces supporting the floatability of the pairs of spheres agree well. The maximum measured forces on the pairs were equal to the sum of the maximum forces measured on two single spheres individually, but the forces measured on the single spheres and their pairs at different depths of interface deformation were different. The vertical forces supporting the floatability of the sphere pairs can better tolerate the interface deformation than the same force on two single particles. This evidence is also supported by the experiments with multiple particles floating at the surface of water-ethanol mixtures. Adding ethanol into water reduced the surface tension of water and the floatability of particles at the water surface, but the floatability of multiple particles was sustainable at much lower critical surface tensions than that for single particles, invalidating the classical theories. Lateral interparticle interactions influence the floatability of particles and should be considered in its modeling.

End Effect on Permeability of Loose Particulate Bed Having Different Internal Structures

Permeability through media having various structures has been studied theoretically. We consider loose porous media, like fibrous materials, and media with a localized pore network, like fractured rocks. We model complicated porous structures by using assemblage of spherical particles. The calculations of permeability are performed by the Stokesian dynamic approach, which enables us to derive fluid motion in the presence of many particles. The Ewald summation technique is employed to represent infinite and finite particulate beds. In the infinite bed where the particles exist endlessly in space, we investigate how the internal structure of the media affects permeability. The results indicate that permeability significantly depends on internal structure, particularly the void geometry. In the finite bed where the particles form a bed with finite thickness, we discuss permeability variance due to the presence of ends. It is found that permeability greatly varies in the vicinity of ends owing to the anisotropy of the flow field, which arises from the presence of ends.

Particle Formation in RAFT‐Mediated Emulsion Polymerization: A Calorimetric Study

AbstractAb initio RAFT‐mediated semi‐continuous emulsion polymerizations with controlled monomer feed have been studied by reaction calorimetry. This online monitoring technique provided detailed information about the onset of the nucleation period in semi‐batch processes for emulsion polymerization of styrene and n‐butyl acrylate. The reactions were carried out under controlled radical polymerization conditions by employing amphipathic macro‐RAFT agents of various degrees of surface activity. For n‐butyl acrylate as well as for styrene the more surface active polymeric macro‐RAFT agents led to higher initial polymerization rates. Polymerizations with hydrophobic macro‐RAFT agents also adapted more quickly to an increased monomer feed than polymerizations with hydrophilic macro‐RAFT agents.This points to the presence of more particles when a hydrophobic macro‐RAFT agent is used. Hydrophobic macro‐RAFT agents demonstrated to be promising for producing latex products with a proper control of particle number and particle size distribution.

Martensitic transformation of Ni 50Ti 45Ta 5 shape memory alloy

Ni 50Ti 45Ta 5 alloy is similar to equiatomic NiTi alloy with near equal transformation temperatures and having B2 ↔ B19′ one stage transformation. The main lattice twin is 〈0 1 1〉 type II twin. The lattice parameter of B2 austenite is a = 0.3025 nm, and the lattice parameters of B19′ martensite is a = 0.290 nm, b = 0.412 nm, c = 0.473 nm and β = 98.2°. The transformation temperature depression of Ni 50Ti 45Ta 5 alloy is larger than that of NiTi alloy under the same number of thermal cycles due to the presence of more particles. The martensite stabilization occurs due to the deformation. It is closely related to the variation of the elastic energy and the irreversible energy during deformation. The Ni 50Ti 45Ta 5 alloy has a higher martensite stabilization than NiTi alloy under the same degree of deformation due to the presence of a soft β-Ta phase.

Direct Simulation of the Motion of Neutrally Buoyant Circular Cylinders in Plane Poiseuille Flow

In this article we discuss the generalization of a Lagrange multiplier-based fictitious domain method to the simulation of the motion of neutrally buoyant particles in a Newtonian fluid. Then we apply it to study the migration of neutrally buoyant circular cylinders in plane Poiseuille flow of a Newtonian fluid by direct numerical simulation. The Segré–Silberberg effect is found for the cases with one and several circular cylinders. In general, it is believed that the migration away from the center of the channel is due to an effect of the curvature of velocity profile. Via direct numerical simulation, we find that this effect is not weakened by the presence of many particles, but by the collisions among the particles. Experiments and simulations for hundreds of circular cylinder cases show that particles concentrate in the central region where the shear rate is low. A power law associated with the horizontal velocity of the mixture of fluid/particles is also presented.

Numerical simulation of the motion of neutrally buoyant particles in the plane Poiseuille flow of a Newtonian fluid

In this note we discuss the generalization of a Lagrange multiplier based fictitious domain method to the simulation of migration of neutrally buoyant particles in plane Poiseuille flow of a Newtonian fluid. The migration away from the center of the channel is believed to be an effect of the curvature of the velocity profile. We found this effect is not weakened by the presence of many particles, but instead by the collisions among the particles. Experiments and simulations show that the particles concentrate in the central region where the shear rate is low.

Evolution of texture, micro structure and mechanical property anisotropy in an Al-Li-Cu alloy

The evolution of hot deformation texture, microstructure and yield strength anisotropy in an Al-Li-Cu alloy AF/C489 was studied in the as-extruded, solution heat treated and peak-aged condition. Cast AF/C489 alloy with a random texture was extruded at six temperatures ranging from 260 to 538°C and immediately quenched to capture texture and microstructure at the extrusion temperature. In the as-extruded condition, significant amounts of the major rolling texture components, namely, Br 112〈110〉, S 123〈634〉 and Cu 112〈111〉 were observed at all extrusion temperatures. However, at extrusion temperatures above 480°C there was a sharp rise in the intensity of Br component. When the extruded alloy was solution treated the Br intensity remained stable for the two highest extrusion temperatures. However, solution heat treatment (SHT) following extrusion at lower temperatures resulted in the loss of all the rolling texture components including Br. Furthermore, the solution heat treatment following extrusion at temperatures below 330°C showed presence of significant amount of ND rotated cube (100〈130〉). It is suggested that formation of Br texture may be due to the development of shear bands. Increase in dynamic recovery at high extrusion temperature enhances the shear banding tendency and consequently increased presence of Br. This is consistent with negligible recrystallization during solution treatment following elevated temperature extrusion as observed by optical microscopy. Significant recrystallization during SHT following low temperature extrusion results in the presence of rotated cube components. This is consistent with the presence of more particles at low temperature as observed by transmission electron microscopy. The yield stress anisotropy in the SHT material is attributed to crystallographic texture in the SHT material whereas in the extruded case the anisotropy is due to the combined effect of particles and texture.

Visual modeling of laser Doppler anemometer signals by moiré fringes

This report describes the employment of moiré patterns to model visually interference phenomena in general and laser Doppler anemometer signals in particular. The modeling includes signals created in dual beam and reference beam anemometers by both single particles and particle pairs. The considerations are extended to visual modeling of multiparticle signals and the decay of signal quality in the presence of many particles. The fringe model of the laser Doppler anemometer is also considered, and moiré patterns are employed to demonstrate the interference fringes in the crossover region of two intersecting laser beams. Gaussian beam properties are taken into account to allow the effects of improperly designed optical systems to be studied. Instructions for using computer generated transparencies to produce the different moiré patterns are provided to allow the reader to study in detail the various interference phenomena described.

Age-Hardened Gold Permalloy and Gold Perminvar

This work is an extension of previous work which showed that the addition of gold to Permalloy caused the precipitation of a gold-rich phase and thereby permitted the control of the coercive force by heat treatment. This addition of a second phase to Permalloy greatly improved the switching speed of the alloy. Some compositions of gold Permalloy had switching speeds four times faster than that of the standard composition. In the present work, some of the details of the precipitation process were studied. It was found that for some specimens annealed at 650°C, the precipitation of the gold-rich phase depended strongly upon cold working. When some alloys containing gold were quenched from the solution temperature and annealed at 650°C for 2 hr, there was little increase in coercivity and the electron micrographs showed practically no precipitation of particles of 1000-A diameter or larger. However, when the material was quenched from the solution temperature, drastically cold rolled and annealed at 650°C, the coercivity was increased substantially and the electron micrographs revealed the presence of many particles having a diameter of 1000 A. Seven percent gold was also added to the Perminvar composition of 43% Ni-34% Fe-23% Co. The alloy behaved in a manner somewhat similar to the gold-Permalloy compositions. Age-hardening appeared in the vicinity of 600°C and square hysteresis loops were obtained. However, the threshold for rapid rotational flux reversal was substantially higher than the coercive force. Consequently, these alloys appeared less desirable for switching applications than Permalloy.